The invention relates to a composition containing at least one surface active compound and glycolipids at least in part in the form of esters and the use of the composition and more generally of a composition containing glycolipids which may be in this derivative form or in crude form in a decontamination process for a medium polluted by hydrocarbons.
Contamination of soils and groundwater tables by hydrocarbons often results from infiltration by a petroleum product following leakage from a tank or a pipe system or from an accidental spillage at ground level. The risks associated with the presence of hydrocarbons in the soil are related, on the one hand to safety, due to risks of explosion of the volatile hydrocarbon vapours, and on the other hand, to the quality of underground water due to the solubilization of aromatic hydrocarbons such as benzene, toluene, xylenes, ethylbenzene, naphthalene and certain aliphatic hydrocarbons such as iso- or cycloalkanes and olefines.
In order to restore a contaminated aquifer a start is generally made by recovering the fluid pollutant on the surface of the ground water table by making it migrate towards a pumping well. Also, it is often necessary to eliminate the residual product trapped in the unsaturated zone and in the beat region as it constitutes a long-term risk.
Various methods employed in situ have been described to eliminate petroleum hydrocarbons in residual quantities in the soil. They consist of either extracting the soil pollutant or of destroying it by biodegradation in situ or a combination of these two treatments. Extraction can be carried out in gas phase by entraining the hydrocarbons with air circulated in the contaminated unsaturated zone by means of a ventilator connected to an extraction well; this technique is only applicable to volatile fractions and can require a long period of operation. Extraction of the residual products has also been proposed by cleansing the contaminated zone with water containing surfactants and by using an input well and a well for the recovery of effluents.
The use of surfactants has also been proposed to activate the biodegradation in situ of residual hydrocarbons by increasing their accessibility to bacteria, nutriments and oxygen.
The surfactants described to facilitate the extraction of hydrocarbons in the form of emulsions in water or to activate their biodegradation are in general non-ionic compounds, for example a polyethoxylated fatty alcohol or a polyethoxylated nonylphenol, or anionic compounds, for example those of the sulphonate family.
However, the use of these surfactants has its own limits due to the fact that it leads to biodegradation rates and elimination rates of the hydrocarbons from the porous medium which are not sufficiently high.
The prior art is for example described in the Patent EP-A-0 499 434 (Unilever), which describes a composition containing a glycolipidic surfactant (sophorolipid) in its crude form (mixture of acid and lactone forms) and an anionic, cationic or non-ionic surfactant, in particular used for its detergent properties during textile washing operations, and Biosis, (AN 90: 154 490) Appl. Microbiol. Biotechnol. vol 32. No. 4, 1990, pages 485-489, ISBN 0 175-7598, which describes the effect of the addition of sophorolipidic surfactants on the degradation of hydrocarbons by bacteria in a soil and on the biomass thus produced.
Other Patent Applications FR-A-2,437,874, EP-A-0,310, 005, GB-A-2, 053, 182 and EP-A-0, 048, 339 also illustrate the prior art.
It has also been found to be advantageous to use formulations of surfactants to simultaneously activate the two process mentioned above, for example non-ionic or anionic surfactants containing a glycolipidic cosurfactant, advantageously from the family of sophorolipids and preferably glycolipids, usually sophorolipids, at least in part in the form of esters. It is also thought that the use of such a compound improves the interfacial properties of the synthetic surfactants, and in particular, increases the lowering of the water-oil interfacial tension, and makes the injected aqueous solution more stable by reducing losses of active ingredient by adsorption on soil particles and, in the case of the use of anionic surfactants, by reducing in particular the colmation of the porous medium resulting from the precipitation of the calcium salts of these compounds in the presence of calcium-containing clay.